Organs and Organ Systems - 6 | Britannica.com Organs and Organ Systems in biology, a group of tissues in a living organism that have been adapted to perform a specific function. Browse Subcategories: (48) Displaying 401 - 500 of 800 results lacteal one of the lymphatic vessels that serve the small intestine and, after a meal, become white from the minute fat globules that their lymph contains (see chyle). The lacteals were described as venae albae et lacteae (“white and milky veins”) by their discoverer,... Langerhans, islets of irregularly shaped patches of endocrine tissue located within the pancreas of most vertebrates. They are named for the German physician Paul Langerhans, who first described them in 1869. The normal human pancreas contains about 1,000,000 islets. The... large intestine posterior section of the intestine, consisting typically of four regions: the cecum, colon, rectum, and anus. The term colon is sometimes used to refer to the entire large intestine. The large intestine is wider and shorter than the small intestine (approximately...

larynx a hollow, tubular structure connected to the top of the windpipe (trachea); air passes through the larynx on its way to the lungs. The larynx also produces vocal sounds and prevents the passage of food and other foreign particles into the lower respiratory... lateral line system a system of tactile sense organs, unique to aquatic vertebrates from cyclostome fishes (lampreys and hagfish) to amphibians, that serves to detect movements and pressure changes in the surrounding water. It is made up of a series of mechanoreceptors... laterality in biological psychology, the development of specialized functioning in each hemisphere of the brain or in the side of the body which each controls. The most obvious example of laterality is handedness, which is the tendency to use one hand or the other... latex colloidal suspension, either the milky white liquid emulsion found in the cells of flowering plants such as the Para rubber tree (Hevea brasiliensis) or any of various manufactured water emulsions consisting of synthetic rubber or plastic. The plant... latissimus dorsi widest and most powerful muscle of the back. It is a large, flat, triangular muscle covering the lower back.

It arises from the lower half of the vertebral column and iliac crest (hipbone) and tapers to a rounded tendon inserted at (attached to) the... leaf in botany, any usually flattened green outgrowth from the stem of a vascular plant. Leaves manufacture food for plants, which in turn ultimately nourish and sustain all land animals. Botanically, leaves are an integral part of the stem system, and they... lens in anatomy, a nearly transparent biconvex structure suspended behind the iris of the eye, the sole function of which is to focus light rays onto the retina. The lens is made up of unusual elongated cells that have no blood supply but obtain nutrients... levator muscle any of the muscles that raise a body part. In humans these include the levator anguli oris, which raises the corner of the mouth; the levator ani, collective name for a thin sheet of muscle that stretches across the pelvic cavity and helps hold the pelvic... levonorgestrel synthetic progestogen (any progestational steroid, such as progesterone) that is used as a form of contraception in women.

Levonorgestrel is the mirror compound (enantiomer) of norgestrel, which was synthesized in the early 1960s by American scientist... lips soft pliable anatomical structures that form the mouth margin of most vertebrates, composed of a surface epidermis (skin), connective tissue, and (in typical mammals) a muscle layer. In man the outer skin contains hair, sweat glands, and sebaceous (oil)... liver the largest gland in the body, a spongy mass of wedge-shaped lobes that has many metabolic and secretory functions. The liver secretes bile, a digestive fluid; metabolizes proteins, carbohydrates, and fats; stores glycogen, vitamins, and other substances;... loop of Henle long, U-shaped portion of the tubule that conducts urine within each nephron of the kidney of reptiles, birds, and mammals. The principal function of the loop of Henle appears to be the recovery of water and sodium chloride from the urine. This function... Ludwig, Carl F. W. a founder of the physicochemical school of physiology in Germany.

A professor of physiology at the universities of Marburg (1846–49), Zürich (1849–55), Vienna (1855–65), and Leipzig (1865–95), Ludwig is best known for his study of the cardiovascular... lung in air-breathing vertebrates, either of the two large organs of respiration located in the chest cavity and responsible for adding oxygen to and removing carbon dioxide from the blood. In humans each lung is encased in a thin membranous sac called the... lymph pale fluid that bathes the tissues of an organism, maintaining fluid balance, and removes bacteria from tissues; it enters the blood system by way of lymphatic channels and ducts. Prominent among the constituents of lymph are lymphocytes and macrophages,... lymphatic system a subsystem of the circulatory system in the vertebrate body that consists of a complex network of vessels, tissues, and organs. The lymphatic system helps maintain fluid balance in the body by collecting excess fluid and particulate matter from tissues... lymphoblast immature white blood cell that gives rise to a type of immune cell known as a lymphocyte.

The nucleus contains moderately fine chromatin (readily stainable nuclear material) and has a well-defined nuclear membrane. There are one or two nucleoli, and... lymphocyte type of white blood cell (leukocyte) that is of fundamental importance in the immune system because lymphocytes are the cells that determine the specificity of the immune response to infectious microorganisms and other foreign substances. In human adults... lymphocytic choriomeningitis inflammation of the meninges (membranes covering the central nervous system) and choroid plexus (an area of the brain that regulates the pressure of cerebrospinal fluid), characterized by marked infiltration of lymphocytes into the cerebrospinal fluid.... lymphoid tissue cells and organs that make up the lymphatic system, such as white blood cells (leukocytes), bone marrow, and the thymus, spleen, and lymph nodes. Lymphoid tissue has several different structural organizations related to its particular function in the... Lyonnet, Pierre Dutch naturalist and engraver famed for his skillful dissections and illustrations of insect anatomy. Trained as an attorney, Lyonnet was a respected biologist and spent most of his time engraving objects of natural history.

He made the drawings for... Macleod, J. J. R. Scottish physiologist noted as a teacher and for his work on carbohydrate metabolism. Together with Sir Frederick Banting, with whom he shared the Nobel Prize for Physiology or Medicine in 1923, and Charles H. Best, he achieved renown as one of the discoverers... macula lutea in anatomy, the small yellowish area of the retina near the optic disk that provides central vision. When the gaze is fixed on any object, the centre of the macula, the centre of the lens, and the object are in a straight line. In the centre of the macula... Magendie, François French experimental physiologist who was the first to prove the functional difference of the spinal nerves. His pioneer studies of the effects of drugs on various parts of the body led to the scientific introduction into medical practice of such compounds... malpighian tubule in insects, any of the excretory organs that lie in the abdominal body cavity and empty into the junction between midgut and hindgut.

In species having few malpighian tubules, they are long and coiled; in species with numerous (up to 150) tubules, they... mammary gland milk-producing gland characteristic of all female mammals and present in a rudimentary and generally nonfunctional form in males. Mammary glands are regulated by the endocrine system and become functional in response to the hormonal changes associated... mandibulofacial dysostosis a rare, genetic disorder, inherited as an autosomal-dominant trait and characterized by some or all of the following: underdevelopment of the cheek and jaw bones, widely separated eyes, malformation of the lower eyelid and lack of eyelashes, malformation... mantle in biology, soft covering, formed from the body wall, of brachiopods and mollusks; also, the fleshy outer covering, sometimes strengthened by calcified plates, of barnacles. The mantle of mollusks and brachiopods secretes the shell in species that possess... marble bone disease rare disorder in which the bones become extremely dense, hard, and brittle. The disease progresses as long as bone growth continues; the marrow cavities become filled with compact bone.

Because increased bone mass crowds the bone marrow, resulting in... marsupium specialized pouch for protecting, carrying, and nourishing newborn marsupial young. A marsupium is found in most members of the order Marsupialia (class Mammalia). In some marsupials (e.g., kangaroos) it is a well-developed pocket, while in others (e.g.,... masseter (from Greek masasthai, “to chew”), prominent muscle of the jaw. The masseter arises from the zygomatic bone (cheekbone) and is inserted at the rear of the mandible (jawbone). Contraction of the muscle raises the mandible, and it is particularly used... mast cell tissue cell of the immune system of vertebrate animals. Mast cells mediate inflammatory responses such as hypersensitivity and allergic reactions. They are scattered throughout the connective tissues of the body, especially beneath the surface of the... mastoid process the smooth pyramidal or cone-shaped bone projection at the base of the skull on each side of the head just below and behind the ear in humans. The mastoid process is important to students of fossil humans because it occurs regularly and in the specific...

mastoiditis inflammation of the mastoid process, a projection of the temporal bone just behind the ear. Mastoiditis, which primarily affects children, usually results from an infection of the middle ear (otitis media). Symptoms include pain and swelling behind the... mechanoreception ability of an animal to detect and respond to certain kinds of stimuli—notably touch, sound, and changes in pressure or posture—in its environment. Sensitivity to mechanical stimuli is a common endowment among animals. In addition to mediating the sense... medulla oblongata the lowest part of the brain and the lowest portion of the brainstem. The medulla oblongata is connected by the pons to the midbrain and is continuous posteriorly with the spinal cord, with which it merges at the opening (foramen magnum) at the base... melanocyte specialized skin cell that produces the protective skin-darkening pigment melanin. Birds and mammals possess these pigment cells, which are found mainly in the epidermis, though they occur elsewhere—e.g., in the matrix of the hair. Melanocytes are branched,...

melorheostosis rare disorder of unknown cause in which cortical bone overgrowth occurs along the main axis of a bone in such a way as to resemble candle drippings. Pain is the major symptom, and stiffness and deformity may result. Usually only one limb and the nearest... meninges three membranous envelopes—pia mater, arachnoid, and dura mater—that surround the brain and spinal cord. Cerebrospinal fluid fills the ventricles of the brain and the space between the pia mater and the arachnoid. The primary function of the meninges... menstruation periodic discharge from the vagina of blood, secretions, and disintegrating mucous membrane that had lined the uterus. The biological significance of the process in humans can best be explained by reference to the reproductive function in other mammals.... mesonephros permanent kidney of amphibians and most fish, developing posterior to and replacing the pronephros of the embryonic and larval stages. It is a paired organ consisting of a set of nephrons having capsules that filter blood from the glomerulus and tubules... metabolic bone disease any of several diseases that cause various abnormalities or deformities of bone.

Examples of metabolic bone diseases include osteoporosis, rickets, osteomalacia, osteogenesis imperfecta, marble bone disease (osteopetrosis), Paget disease of bone, and... metacarpal any of several tubular bones between the wrist (carpal) bones and each of the forelimb digits in land vertebrates, corresponding to the metatarsal bones of the foot. Originally numbering five, metacarpals in many mammals have undergone much change and... metanephros permanent kidney in reptiles, birds, and mammals, developing by the 10th week in human embryos from the lower part of the Wolffian duct, and replacing the embryonic structure called the mesonephros. It consists of a compact, paired organ containing many... metatarsal any of several tubular bones between the ankle (tarsal) bones and each of the hindlimb digits, in land vertebrates corresponding to the metacarpal bones of the hand (forepaw). In humans the five metatarsal bones help form longitudinal arches along the... metatarsalgia persistent pain in the metatarsal region, or ball, of the foot.

The condition arises when the weight of the body, while standing, is forced to rest on the centre of the anterior arch (on the heads of the central metatarsal bones) instead of on the inside... microglia type of neuronal support cell (neuroglia) occurring in the central nervous system of invertebrates and vertebrates that functions primarily as an immune cell. Microglia were first identified by histological staining with silver carbonate between 1919... midbrain region of the developing vertebrate brain that is composed of the tectum and tegmentum. The midbrain serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing. It is located within the brainstem... Mirbel, Charles-François Brisseau de French botanist whose book Traité d’anatomie et de physiologie végétale, 2 vol. (1802; “Treatise on Plant Anatomy and Physiology”), earned him recognition as a founder of plant cytology and plant physiology. His most notable contribution to plant cytology... mirror neuron type of sensory-motor cell located in the brain that is activated when an individual performs an action or observes another individual performing the same action.

Thus, the neurons “mirror” others’ actions. Mirror neurons are of interest in the study... Mohl, Hugo von German botanist noted for his research on the anatomy and physiology of plant cells. Von Mohl received his degree in medicine from the University of Tübingen in 1828. After studying for several years at Munich, he became professor of botany at Tübingen... Moleschott, Jacob physiologist and philosopher noted for his belief in the material basis of emotion and thought. His most important work, Kreislauf des Lebens (1852; “The Circuit of Life”), added considerable impetus to 19th-century materialism by demanding “scientific... Mondino de’ Luzzi Italian physician and anatomist whose Ana tho mia Mundini (MS. 1316; first printed in 1478) was the first European book written since classical antiquity that was entirely devoted to anatomy and was based on the dissection of human cadavers. It remained...

mononuclear phagocyte system class of cells that occur in widely separated parts of the human body and that have in common the property of phagocytosis, whereby the cells engulf and destroy bacteria, viruses, and other foreign substances and ingest worn-out or abnormal body cells.... Monro, Alexander, primus physician, first professor of anatomy and surgery at the newly founded University of Edinburgh medical school. With his son, Alexander secundus (1733–1817), and his grandson, Alexander tertius (1773–1859), who succeeded him in the chair at Edinburgh,... Monro, Alexander, secundus physician who, with his father, Alexander primus (1697–1767), and his son, Alexander tertius (1773–1859), played a major role in establishing the University of Edinburgh as an international centre of medical teaching. Appointed to the chair of anatomy... Morgagni, Giovanni Battista Italian anatomist and pathologist whose works helped make pathological anatomy an exact science. After graduating in 1701 at Bologna with degrees in philosophy and medicine, Morgagni acted as prosector to A.M.

Valsalva, whom he assisted in preparing... mouth in human anatomy, orifice through which food and air enter the body. The mouth opens to the outside at the lips and empties into the throat at the rear; its boundaries are defined by the lips, cheeks, hard and soft palates, and glottis. It is divided... mouthbreeder any fish that breeds its young in the mouth. Examples include certain catfishes, cichlids, and cardinal fishes. The male of the sea catfish Galeichthys felis places up to 50 fertilized eggs in its mouth and retains them until they are hatched and the... mucous membrane membrane lining body cavities and canals that lead to the outside, chiefly the respiratory, digestive, and urogenital tracts. Mucous membranes line many tracts and structures of the body, including the mouth, nose, eyelids, trachea (windpipe) and lungs,... mucus viscous fluid that moistens, lubricates, and protects many of the passages of the digestive and respiratory tracts in the body. Mucus is composed of water, epithelial (surface) cells, dead leukocytes, mucin, and inorganic salts.

Mucus is produced by... Müller, Johannes German physiologist and comparative anatomist, one of the great natural philosophers of the 19th century. His major work was Handbuch der Physiologie des Menschen für Vorlesungen, 2 vol. (1834–40; Elements of Physiology). Müller was the son of a shoemaker.... multiple myeloma malignant proliferation of cells within the bone marrow that usually occurs during middle age or later and increases in occurrence with age. Myelomas are slightly more common in males than in females and can affect any of the marrow-containing bones,... Murad, Ferid American pharmacologist, who, along with Robert F. Furchgott and Louis J. Ignarro, was co-awarded the 1998 Nobel Prize in Physiology or Medicine for the discovery that nitric oxide (NO) acts as a signaling molecule in the cardiovascular system. Their... Murray, Joseph E. American surgeon who in 1990 was cowinner (with E. Donnall Thomas) of the Nobel Prize for Physiology or Medicine for his work in lifesaving organ- and tissue-transplant techniques.

Murray received a bachelor of arts degree (1940) from Holy Cross College,... muscle contractile tissue found in animals, the function of which is to produce motion. Movement, the intricate cooperation of muscle and nerve fibres, is the means by which an organism interacts with its environment. The innervation of muscle cells, or fibres,... muscle disease any of the diseases and disorders that affect the human muscle system. Diseases and disorders that result from direct abnormalities of the muscles are called primary muscle diseases; those that can be traced as symptoms or manifestations of disorders... muscle system, human the muscles of the human body that work the skeletal system, that are under voluntary control, and that are concerned with movement, posture, and balance. Broadly considered, human muscle—like the muscles of all vertebrates—is often divided into striated... mycelium the mass of branched, tubular filaments (hyphae) of fungi. The mycelium makes up the thallus, or undifferentiated body, of a typical fungus. It may be microscopic in size or developed into visible structures, such as brackets, mushrooms, puffballs, rhizomorphs...

myelin white, insulating sheath on the axon of many neurons. Composed of fatty materials, protein, and water, the myelin sheath is deposited in layers around axons by Schwann cells in the peripheral nervous system and by a type of neuroglia called an oligodendrocyte... myeloblast immature blood cell, found in bone marrow, that gives rise to white blood cells of the granulocytic series (characterized by granules in the cytoplasm, as neutrophils, eosinophils, and basophils), via an intermediate stage that is called a myelocyte.... myofibril very fine contractile fibres, groups of which extend in parallel columns along the length of striated muscle fibres. The myofibrils are made up of thick and thin myofilaments, which help give the muscle its striped appearance. The thick filaments are... nail in the anatomy of humans and other primates, horny plate that grows on the back of each finger and toe at its outer end. It corresponds to the claw, hoof, or talon of other vertebrates. The nail is a platelike, keratinous, translucent structure that...

nasal gland in marine birds and reptiles that drink saltwater, gland that extracts the salt and removes it from the animal’s body. Its function was unknown until 1957, when K. Schmidt-Nielsen and coworkers solved the long-standing problem of how oceanic birds can... nematocyst minute, elongated, or spherical capsule produced exclusively by members of the phylum Cnidaria (e.g., jellyfish, corals, sea anemones). Several such capsules occur on the body surface. Each is produced by a special cell called a cnidoblast and contains... nephridium unit of the excretory system in many primitive invertebrates and also in the amphioxus; it expels wastes from the body cavity to the (usually aquatic) exterior. The evolution of nephridia encouraged tissue specialization by eliminating the need for all... nephron functional unit of the kidney, the structure that actually produces urine in the process of removing waste and excess substances from the blood. There are about 1,000,000 nephrons in each human kidney. The most primitive nephrons are found in the kidneys...

nerve net primitive nerve arrangement forming the entire nervous system of many cnidarians and a part of more advanced nervous systems. Cytoplasmic processes join the nerve cells (neurons) of nerve nets. In cnidarians the neurons are joined to epithelial receptors... nervous system organized group of cells specialized for the conduction of electrochemical stimuli from sensory receptors through a network to the site at which a response occurs. All living organisms are able to detect changes within themselves and in their environments.... nervous system, human system that conducts stimuli from sensory receptors to the brain and spinal cord and that conducts impulses back to other parts of the body. As with other higher vertebrates, the human nervous system has two main parts: the central nervous system (the... neural stem cell largely undifferentiated cell originating in the central nervous system. Neural stem cells (NSCs) have the potential to give rise to offspring cells that grow and differentiate into neurons and glial cells (non-neuronal cells that insulate neurons and... neurofibromatosis either of two hereditary disorders characterized by distinctive skin lesions and by benign, progressively enlarging tumours of the nervous system.

Neurofibromatosis type 1, also known as von Recklinghausen’s disease, is much the more common of the two... neurogenic arthropathy condition characterized by the destruction of a stress-bearing joint, with development of new bone around the joint. Eventually the affected individual is unable to use the joint but experiences little or no pain or discomfort. The condition accompanies... neuroglia any of several types of cell that function primarily to support neurons. The term neuroglia means “nerve glue.” In 1907 Italian biologist Emilio Lugaro suggested that neuroglial cells exchange substances with the extracellular fluid and in this way exert... neurohormone any of a group of substances produced by specialized cells (neurosecretory cells) structurally typical of the nervous, rather than of the endocrine, system. The neurohormones pass along nerve-cell extensions (axons) and are released into the bloodstream... neuromuscular junction site of chemical communication between a nerve fibre and a muscle cell. The neuromuscular junction is analogous to the synapse between two neurons. A nerve fibre divides into many terminal branches; each terminal ends on a region of muscle fibre called...

neuron basic cell of the nervous system in vertebrates and most invertebrates from the level of the cnidarians (e.g., corals, jellyfish) upward. A typical neuron has a cell body containing a nucleus and two or more long fibres. Impulses are carried along one... neuroplasticity capacity of neurons and neural networks in the brain to change their connections and behaviour in response to new information, sensory stimulation, development, damage, or dysfunction. Although neural networks also exhibit modularity and carry out specific... neurosecretory cell a type of neuron, or nerve cell, whose function is to translate neural signals into chemical stimuli. Such cells produce secretions called neurohormones that travel along the neuron axon and are typically released into the bloodstream at neurohemal organs,... neurotransmitter any of a group of chemical agents released by neurons (nerve cells) to stimulate neighbouring neurons, thus allowing impulses to be passed from one cell to the next throughout the nervous system. The site where neurons meet is called the synapse and... nevus congenital skin lesion, or birthmark, caused by abnormal pigmentation or by proliferation of blood vessels and other dermal or epidermal structures.

Nevi may be raised or may spread along the surface of the skin. In other types, such as the blue nevus,... node of Ranvier periodic gap in the insulating sheath (myelin) on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses. These interruptions in the myelin covering were first discovered in 1878 by French histologist and pathologist... normoblast nucleated normal cell occurring in red marrow as a stage or stages in the development of the red blood cell (erythrocyte). Some authorities call the normoblast a late-stage erythroblast, the immediate precursor of the red blood cell; others distinguish... nose the prominent structure between the eyes that serves as the entrance to the respiratory tract and contains the olfactory organ. It provides air for respiration, serves the sense of smell, conditions the air by filtering, warming, and moistening it, and... occipital bone forming the back and back part of the base of the cranium, the part of the skull that encloses the brain. It has a large oval opening, the foramen magnum, through which the medulla oblongata passes, linking the spinal cord and brain.

The occipital... odour the property of certain substances, in very small concentrations, to stimulate chemical sense receptors that sample the air or water surrounding an animal. In insects and other invertebrates and in aquatic animals, the perception of small chemical concentrations... oidium in fungi (kingdom Fungi), a single-celled asexual spore (arthrospore) produced by fragmentation of fungal filaments (hyphae) in lower fungi; the asexual stage of Erysiphaceae (powdery mildew fungi); or, in Basidiomycota, both an asexual spore (microconidium)... Human Anatomy Muscles: How Muscles Are Named & Why Size When it comes to size, muscles are large or small, short or long, or wide. The largest muscle in a related group of muscles is often referred to as maximus or magnus. An example that you're familiar with is the gluteus maximus. Gluteus is Latin for your rear end -- or more politely, your buttock. Thus, gluteus maximus identifies the largest muscle in your butt--the one you feel when you squeeze the cheeks of your butt together.

Another example is the adductor magnus, which is the large muscle running down the inner thigh that pulls the leg back in from the side. You can feel this muscle if you balance against a table, putting your hand against the inside of the opposite thigh and then resisting as that hand tries to push the leg out to the side. Minimus, not surprisingly, refers to the smallest of a group. Thus gluteus minimus identifies the smaller butt muscle located underneath its maximus big brother. Longus, as you might suspect, refers to the longest of a group--as in the adductor longus, which is thinner than the adductor magnus and runs essentially parallel to it. Brevis identifies the shortest of a group. The adductor brevis runs across the thigh to assist in pulling the thigh in towards your body's midline as opposed to down the length of your inner thigh as do the adductor magnus and minimus. In Latin, the word "latus" means "side." Thus latissimus identifies the largest muscle "in width" in a group. Latissimus dorsi is the name of the large muscles that run from under your arms, across your "sides," and then across the middle of your back.

Bodybuilders refer to these as their "lats." So again, quick review, when it comes to size, the key identifiers are maximus or magnus, minimus, longus, brevis, and latissimus. Shape There are really only four shapes that you need to concern yourself with when it comes to naming muscles: trapezoids, triangles, saw tooth, and flat. A trapezoid is like a rectangle, but with only two sides that are parallel as opposed to all four. For simplicity you can think of it as an oddly shaped rectangle. The trapezius is the large distorted rectangle that sits on the upper portion of the back and is rotated 45% so that one corner attaches to each shoulder, one at the top of the neck, and the fourth corner to the middle of the back. I actually think it looks more diamond shaped, but I didn't discover it, so I didn't get to name it. The fourth letter in the Greek alphabet is delta, which is drawn in the shape of a triangle Δ. Deltoid, then, refers to the triangular shaped muscle that sits on the top of the shoulder.

The Latin verb for saw is "serrare." In anatomy, then, serratus means saw-toothed in shape. Serratus anterior is the name of the muscle that holds your scapula (shoulder blade) to your ribs. It gets its saw-like appearance from the pattern it makes is it attaches to each individual rib. The French word for flat is "plat." Think of the word plateau. The platysma muscle is the broad, thin, flat muscle that has its origin across the middle of your chest, runs up across the front and sides of your neck and ends at your chin. Its primary role is to hold the other muscles of the neck in place and help with facial expressions. It comes into play when you tense your jaw and neck. Orientation of the Muscle Fibers Orientation refers to how the muscle fibers line up to the midline of the body. This makes it pretty simple. They can only be parallel, perpendicular, or diagonal to that line. Rectus is the word used to identify those muscles whose fibers run parallel to the midline.

The Latin word for "right" is "rectus." Rectus abdominis, for example, identifies the six-pack abdominal muscle that runs down the front of the stomach--with its fibers running parallel to the spine. I have to admit, getting parallel out of rectus is a bit of a stretch. Its original root, as I mentioned, is in the Latin word for "right or true." Think of the word rectitude which identifies the quality of being virtuous or straight. Well, from that you get "rectus" as identifying a muscle that runs straight and true -- or dare I say: parallel. Don't blame me. Nobody ever said all doctors were Latin scholars. These are the famous "six-pack" muscles. They get that name because, when well developed, the muscle gets segmented by bands of cartilage that give the muscle the appearance of having six separate sections. Oblique comes from the old French and means "at an angle." Thus we have both the external and internal obliques of the abdomen, which run one on top of the other, with their fibers running at an angle to the midline and perpendicular to each other.

These are the muscles just to the outside of your six-pack, and these are the muscles you work when you do sit ups and touch each elbow to the opposite leg. Transverse means crosswise or perpendicular to the midline of the body. Thus we have the transversus abdominis. From the name, you can pretty much guess that they're located in the abdomen and which direction their fibers run. In fact, these muscles are located in the sides of the abdomen, underneath the obliques. And the fibers do indeed run across the body. And it's these muscles you feel when you stretch from side to side. Mechanical Action of the Muscle Here we're talking about what the muscle does. Does it flex, extend, turn up, turn something down, lift it up, lower it, rotate around a joint, move body parts away from a midline or pull them back towards the midline, make an area rigid, or close an opening? The action that a muscle performs is often used in naming that muscle. Flexor muscles decrease the angle at a joint. The flexor pollicis longus is the muscle in the forearm that pulls on the thumb and bends or flexes it inward toward the palm.

We already know that longus means it's the longest muscle in its group -- and, in fact, it runs the full length of the forearm from the elbow to the thumb. And "pollicis" is Latin for thumb. Thus, the name tells us that it's the long muscle that flexes the thumb. Extensors are the muscles that counter flexors. They increase the angle at a joint. The extensor pollicis longus, therefore, is the long muscle in the forearm that straightens out the thumb once it's been bent inward. Pronators turn limbs so that they face downwards or backwards. If you hold your arm out in front of you, palm up, it's the pronator teres muscle that allows you to turn the arm at the elbow so that the palm is now facing downwards. The Latin word "pronus" means "face down" -- as in lying prone. And "teres" is Latin for "rounded or cylindrical," which refers to the shape of the muscle. The counter to a pronator is a supinator. The musculus supinator, for example, is the muscle in your forearm that turns your palm back facing up after you've pronated it down.

Supinator comes from the Latin word supinum, which means "lying on your back." Levators, as is obvious from the word, are muscles that lift things up. The levator ani is the muscle that pulls the anus up at the end of the digestive tract. If that muscle starts to weaken, you can feel the anus starting to push out and down -- very uncomfortable. Depressors, as would be expected, are the opposite of levators; they push or pull things downward. The depressor labii inferioris is the muscle located below (or inferior) to the lips that pulls the lower lip down. Rotators, as the name implies, produce a circular movement around a joint -- the rotator cuff in the shoulder being the most obvious example. Abductor muscles move bones away from a midline in the body. The term is used both generically to describe the action of any muscle that moves away from the midline (the gluteus medius, for example, is an abductor in that its action is to pull the thigh out from the midline) and as part of the formal name of a handful of muscles such as the abductor pollicis brevis, which pulls the thumb away from the palm.

Adductors move the bones back towards the midline as we saw with both the adductor longus and the adductor brevis, which are located in the inner thigh and that we looked at previously. Tensor muscles make things rigid. The tensor fascia lata muscle in the leg tightens and gets rigid to support the knee. Sphincters close openings, as does the anal sphincter. Number of Points of Origin A small number of muscles are named after the number of points of attachment they have at their points of origin. These would be: The biceps brachii in your arm that has two points of origin. Brachii is Latin for branches -- thus, your biceps muscle has two branches at its origin. The triceps brachii in your arm has three points of origin. And the quadriceps in your leg has four points of origin. Origin and Insertion An even smaller number of muscles are named after the parts of the body where they start and end -- their origin and insertion. The sternocleidomastoid muscle, for example, originates from both the sternum and clavicle (breastbone and collarbone) and inserts into the mastoid bone (just below the ear).

Named by Function And a small number of muscles are named after their function. The risorius is a facial muscle that is crucial for the expressions of smiling and laughter. Humans are the only animals that have a well developed risorius. Risorius comes from the Latin word "risus," which means "laugh." Masseter comes from the Greek word for "chew," and that's its function in the human jaw. The sartorius muscle (from the Latin word for "tailor") runs from the outer hip, across the thigh, and ends at the inner knee. This muscle pulls the leg up at the knee while simultaneously turning it inward. It is used to cross the legs in the manner of an old time tailor sitting on the floor and sewing hides together--hence the name. Location And finally, some muscles are named by where they are found in the body. The temporalis muscle is named after the temporal bone (your temple) on top of which it is located. Likewise, the zygomatic bone is your cheekbone, and the zygomaticus muscles are located over your cheekbone.

Review of the major muscle groups Now that we know how muscles are named, let's quickly work through the body and take a look at the major muscle groups Upper body front Pectoralis major muscles originate in the sternum and clavicle. They attach under the arm and pull the arms up across the body and rotate them inward. These are your pecs. They are worked by butterflies and bench presses. The deltoid originates in the clavicle, with insertion in the arm below the shoulder. The deltoid elevates the arm when it contracts. Biceps brachii and brachialis work in tandem, attaching in the forearm, and lifting the forearm. Rectus abdominis is a paired muscle that runs down either side of the abdomen. It is supported by tendons that give the muscle the appearance of being segmented -- thus the six pack. Thigh muscles Adductor magnus and longus, which pull the legs together at the midline Rectus femoris, which helps you kick Vastus lateralis and vastus medialis, which along with the rectus femoris help extend the knee and form a cage around it.

Back The trapezius and latissimus dorsi, joined by a mass of tendons, pull across the back. Under the scapula are the Infraspinatus, teres minor, and teres major, which all serve to stabilize the shoulder blades so that the shoulders can move. Gluteus maximus and the gluteus minimus hidden underneath the maximus are primarily stabilizing muscles. They support the pelvis and the trunk where it sits on the femur (the thigh bone). These muscles are most noticeable when standing on one leg. Without special exercise--squats, lunges, and backward leg lifts--they tend to lose tone as we age. This is the saggy butt often associated with aging. Hamstrings: semitendinosus and biceps femoris (not to be confused with the biceps brachii in your arm) -- to flex the lower leg at the knee. (Semitendinosius comes from the Latin words for "half tightly stretched" and refers to normal tightness of the calf muscles.) Calf muscles: gastrocnemius, with its two heads -- medial and lateral.

(Gastrocnemius comes from the Greek and Latin words for calf.) Face and Neck Sternocleidomastoid muscles flex and rotate the head. Omohyoid muscles are used primarily in chewing and swallowing. Sternohyoid helps control the hyoid bone, which plays a key role in swallowing and speech. Thyroid cartilage. Conclusion Let's look back at a couple of key pieces of information that we explored today and see what principles we can draw from them that might be useful in optimizing our own health. Developing Muscles in Balance First, early in the newsletter we explored in some detail that all muscle movement is based on the principle of levers, activated by contracting muscles -- and that to get movement in opposite directions, we need opposing pairs of muscles that pull the levers in opposite directions when they contract. Thus, biceps bend our arms up and triceps straighten them out. This brings us to our first key concept: balance. When you work one set of muscles--say the biceps--you need to work their counterparts--in this case, the triceps. This is not just a matter of looking pretty for bodybuilding competitions; it's a question of long term fitness.

When muscles are not developed in balance: It stresses bones in only one direction, which causes bones to build in an unsound manner. Remember, bones build in response to stress--both gravitational and exercise induced. All muscles attach to bones and pull on those bones, using those bones as levers. If, for example, you continually work your biceps without developing your triceps, your muscles are overwhelming pulling on your arm bones in only one direction. This causes the bone to develop strength on one side, and weakness on the other. (We'll soon explore how bones build in response to stress, which is why weight bearing exercise is so important.) Prolonged, uneven stress on bone is a prescription for serious bone curvature or even a predisposition for breakage down the road. It also should be noted that developing muscles that are out of balance is a prescription for chronic muscle aches and pains as the over developed muscles continually pull and tweak their underdeveloped counterparts. And it's bad for spinal alignment. If your core muscles are not developed equally (or not at all), they will pull the spine in one direction or the other, rather than stabilize it in the proper alignment. This guarantees chronic back pain and even disc problems in time.

Muscle Cages Our muscles also tend to work as protective cages in several areas of our body. These cages not only protect those sensitive areas from damage, they also support and stabilize those areas to protect them from going out of alignment and chronic pain. Two key areas stand out: your lower back and your knee. The core muscles of your stomach (rectus abdominis, transversus abdominis, and the obliques) and your back (the latissimus dorsi) not only protect your internal organs and hold them in place; they also literally hold your spine in correct alignment. If those muscles weaken or develop an imbalance, you can pretty much guarantee, you'll be dealing with chronic back pain. As for your knee, a cage of muscles and their tendons runs from the thigh to the lower leg protecting the knee from instability and injury. Damage to these muscles and tendons requires extensive physical therapy; otherwise the knee will never recover its full strength. Medial and lateral ligaments also help stabilize the knee, as do anterior and posterior ligaments -- all of which can be injured. The real protection for your knee, though, is this cage of tendons that come from the muscles of your thigh.

The stronger those muscles are the stronger that cage is. And keeping in mind that painful knees are one of the biggest reasons people have difficulty walking as they age, keeping those muscles toned and in balance makes all the sense in the world. And this is especially important after any injury--no matter your age. For example, when you are injured and become immobile, the huge muscles of the thigh, such as the quadriceps are the first muscles to atrophy. Without extensive physical therapy, they will never fully recover, which means that your knee is now more prone to injury because its cage is compromised. Next Newsletter In the next issue, we'll conclude our examination of human musculature by talking about the principles of exercise. You will want to read this newsletter if you are concerned about your health. Muscles are not just for good looks. They: Give us strength. Make bones stronger. Hold your spine in line and your organs in place. Protect you from falling. The stronger your legs muscles are, the less likely you are to be unsteady and fall as you age. Protect you even if you do fall. Muscle is dense tissue. If your hip is surrounded by toned muscle, when you fall, it cushions your hip bone and protects it from breaking.

Keep you independent longer as you age. Specifically, we'll explore the different types of muscle fibers we have and how certain exercises can selectively change the balance of those fibers in our muscles -- emphasizing one kind of fiber over another. It's what allows one set of exercise to develop a group of muscles that are suitable for a bodybuilder, while another set makes the same group of muscles suitable for a sprinter. And for those of us who are not professional athletes, understanding muscle fibers and how to exercise them is what allows us to tune our bodies to maximize the lifestyle that we actually lead -- assuming we're not couch potatoes. Muscle Groups Articles and Videos - Bodybuilding.com Muscle Groups 10k views Picture-Perfect Glutes And Ab Workout | Danielle Belanger Latest in Muscle Groups Back Workout Craig Capurso's Ultimate Back Workout Forget that "3 sets of 10" mentality. Let IFBB pro Craig Capurso take you on a heavy-weight, Tabata-style tour of a back workout that will improve your power, strength, muscle size, and muscle endurance. Muscle Groups Get A Crazy Pump And Serious Conditioning In 45 Min This routine is the cure for your boring upper-body-and-cardio workout.

Build muscle in your arms and shoulders, explosiveness in your legs, and athlete-grade conditioning everywhere! Muscle Groups Get Muscle: Your Guide To Putting On Max Size! Understand the 5 critical variables linked to hypertrophy, then put them to work in this expertly created mass-building workout. Chest Workout Brandan Fokken's Best Chest Workout Hit every part of your chest from different angles with lots of reps and as much weight as you can stand. This one is going to set your chest on fire in a good way. Muscle Groups Hunter Labrada: The Son Of Bodybuilding Royalty Comes Of Age Up-and-coming competitor Hunter Labrada tells his story of progressing from shrimp to champ. Watch his profile video, then try his favorite workout for all-around shoulder growth! Muscle Groups The Leg Workout Even The Pros Fear Take 4 common leg exercises and tweak each one to make it as challenging as humanly possible. Now, we're talking serious growth! Muscle Groups Muscle Up With Minimum Equipment The rack-free bodybuilding gym is all about doing more with less. Grow in your garage with these three pieces of equipment and three workouts.

Muscle Groups Evan Centopani's Switched-On Back Workout With one simple tweak, this bread-and-butter barbell routine becomes easier on your lower back but harder on your muscles. You need to know this! Arm Workout Ultimate Arms: How To Build Sleeve-Splitting Biceps And Triceps Want to push your biceps and triceps to their absolute limit in the gym? Cellucor's Craig Capurso uses a kitchen-sink approach to arm obliteration. Arms Brandan Fokken's Inspiring Story And Quick Upper-Body Routine Need a double dose of life inspiration and workout motivation? Watch Brandan Fokken's amazing life story now, then save his quick arm workout for whenever you need! Arm Workout Jason Wittrock's Blow-Your-Arms-Up Workout The most intense arm workout you'll do this year is right here. With nothing more than some dumbbells and a single cable stack, you'll get the pump of your life. Are you ready to earn it? Muscle Groups 5 Insider Techniques For Building The Ultimate Chest You're no rookie, so forget the bench-press basics!

Cellucor athlete Craig Capurso and Bill Geiger are here to serve up some of the best chest-training advice you probably never considered. Muscle Groups Nice Tri: What's Really Wrong With Your Triceps Training Letting certain joints or bones get slightly out of position can mean losing inches of upper-arm gains! Fix these problems, then go back in the gym to tri again. Muscle Groups The Gritty Workout Your Upper Body Needs Are you constantly chasing down new exercises to fill out your workouts? There's a better way! Take the classics and make them feel brand new with these simple tweaks. Muscle Groups Hunter Labrada's High-Volume Back and Biceps Workout Pile on the pulls until your lats and upper back are cooked but your arms are primed for action. That's the recipe for an upper body that will put any T-shirt to the test! Muscle Groups Beginner Bro's Guide To The Gym: Upper Body Just starting out? Don't just ask the biggest dude in your gym to show you the ropes. Ask the Buff Dudes! This is their favorite upper-body workout to help young bucks grow upâand outâthe right way!

Load More Muscle Groups Quad Almighty: The Leg Pre-Exhaust From Hell Tired of running through the same leg-day routine? Flip the script with this leg pre-exhaust workout for the biggest quadriceps pump of your life! Muscle Groups The Simple Way To Make Leg Curls More Effective Conventional gym wisdom may have told you to do this lower-body staple one way, but it may be wrong. Drop the weight, slow down, and get ready to grow! Muscle Groups Shift Your Back Training Into Overdrive! Take a stale back workout and supercharge it by making just one key change to each exercise. Muscle Groups Are Traps Best Trained With Back Or Shoulders? The trapezius muscles come into play when doing both back and shoulder exercises. Learn how and when to train each trap region to ensure maximum development. Muscle Groups Should You Train Rear Delts On Shoulder Or Back Day? The little muscles you're led to believe you don't train enough might already be getting hit twice in your split. Here's what to keep in mind when training the rear delts.

Muscle Groups Tom Graff's 6-Point Plan For Massive Delts If you're wondering why your shoulders won't grow, perhaps they're just not hearing the message. Turn up the volume with this routine! Muscle Groups Want Bigger Pecs? Do Your Workout In Reverse! Flip the script with pre-exhaust training for the best chest pump you'll ever get! Muscle Groups Fix Your 5 Biggest Chest Blunders Unfortunately, building the chest of your dreams requires slightly more than just bench, fly, and getting out the tape measure. Fix these common training mistakes for better chest workouts every time! Muscle Groups Go Heavy With Your Abs This Offseason! Strength coach Cade Cowdin's approach to building thicker, stronger abs during the fall and winter will make you the envy of the beach by summer. It might help you hit big numbers on the major lifts, too! Muscle Groups Redefine Your Abs 4 Brutal Minutes At A Time! Performance coach and celebrity trainer Ron "Boss" Everline has the ab-defining workout you've been seeking. But get ready to burn: These 4 minutes make Tabata-style cardio seem like a breeze by comparison!

Muscle Groups 5 Core Moves Every Athlete Needs Whether you want to push or pull heavy loads, your foundation requires a strong core. Here's how to build one that goes the distance in CrossFit, general weightlifting, or any sport! Muscle Groups Jordan Edwards' Secrets For Instagram-Worthy Abs Cellucor athlete and fitness model Jordan Edwards shares the secrets of her insane ab development. Burn, baby, burn! Muscle Groups The Perfect Home-Gym Back Attack If you train with minimal equipment, back training can seem like a puzzle. Curtis Bartlett's routine is the solution! You'll build strength and size, and then wrap it up with a quick but brutal finisher! Muscle Groups Lais DeLeon's Shoulder Showdown Build healthy, beautiful shoulders with this workout you can do in any gym! Muscle Groups 5 Movement Upgrades You Can Use Today The same old strength training will get you the same old results. Get the most out of every minute in the gym and send your body an unmistakable message to grow by making these simple changes! Muscle Groups Why Full-Body Workouts Make You Stronger Are you setting yourself behind the eight ball by training either too rarely or too often?

Here's how to build your week so you can take your strength where you've dreamed! Muscle Groups 5 Best Shoulder Workouts For Mass: An Intermediate Guide! Progressing from beginner to intermediate means new delt movements and more training volume. Here are 5 new routines that'll keep the gains coming. Load More Muscle Groups 4 Unique Ways To Get Stronger! Building strength for the long haul doesn't have to mean training like a powerlifter. Try these four novel approaches to moving more weight! Muscle Groups 5 Under-The-Radar Chest-Training Tips! Suffering from a case of shallow chest development? Bench-press max got you down? Build a bigger chest and a much stronger bench with these 5 unique training tips! Muscle Groups Katie Chung Hua's Sexy-Arms Workout Want a toned set of arms, but don't always have extra time for the gym? Get results on the double with this all-in-one workout that targets your shoulders, biceps, and triceps! Muscle Groups Shoulder Workouts For Men: The 7 Best Routines For Bigger Delts Whatever your goal, one of these 7 mass-building shoulder workouts can help you achieve it!

Muscle Groups 8 Techniques To Build Monster Quads If your backside is big enough but you want more from your upper legs, check out these 8 quad-building techniques! Muscle Groups 9 Most Underrated Shoulder-Training Tips Building boulder shoulders is about way more than heaving heavy weight overhead. Train smart, stay healthy, and add size with these 9 underrated training tips! Muscle Groups 5 Best Leg Workouts On BodySpace! Wheels feeling deflated? These 5 killer BodySpace workouts are guaranteed to add some size and strength to your lower body! Muscle Groups Build Gorgeous Glutes With Ashley Hoffmann Flat butts are out, and muscular curves are in! Put some bump in that pencil skirt with Ashley Hoffmann's bootylicious tips and workout. Muscle Groups 6 Weeks To Sick Arms Sun's out, guns out! Grow like a pro with the ultimate science-based program for insane gains. Load More What are the systems of the human body?

11 Human Body Systems and Functions ~ Biology Exams 4 U Average weight of a new bone child: 2.6 Kg Body weight (Average)-70Kg Chromosomes-46 Chemical composition of 1 kg fat-free body mass of an adult:720 g water, 210 g protein, 22.4 g Ca, 12 g P, 2.7 g K, 1.8 g Na, 1.8 g Cl, 0.47 g Mg Oxygen: Element is present in maximum amount in human body Teeth: Humans dentition is described as thecodont, heterodont and diphyodont. Thecodont: Teeth are placed in the socket of jaw bones Heterodont : teeth are four different types both in structure and function Diphyodont: Teeth appear twice in the life time of human. They are milk teeth and permanent teeth. Adult Teeth and Baby Teeth Dental formula: An adult human being has 16 teeth on each jaw. In each half of jaws starting from the middle and going backwards, there are two incisors, one canine, two premolars and three molars (2+1+2+3).

Milk teeth: 20 in number (2+1+2) Hardest part: Enamel of tooth 1. Integumentary System The Integumentary system, consisting of the skin, hair and nails, acts as barrier to protect the body from the outside world.It also functions to retain body fluids, protect against disease, eliminates waste products, and regulate body temperature. Skin is the largest organ in the body. Healthy skin has a mean pH of 5.5. This natural acidity is responsible for maintaining the skin's natural flora and protecting against bacterial or fungal colonization. Histology of skin Structurally, skin consists of two layers: Epidermis and dermis. Accessory organs of Skins: Hair and Nails Glands: Sweat (Sudoriferous) glands and Sebaceous glands Thinnest skin: Conjunctive in Eye 2. The Digestive System/Alimentary system Digestive system is well developed and consists of alimentary canal and associated glands. Digestive System Liver Biggest internal organ in the human body Largest gland, weighs about 1.5 kg in man. It is about 1/40th of the total body weight.

Physiological most active organ Digestive System Quiz -> Digestive System MCQ 3. The Respiratory System Oxygen is necessary for the oxidation of nutrients. Body gets oxygen through respiratory gas exchange. The process by which oxidation of nutrients take place in the living cell is known as respiration.It is the step by step oxidation of food materials to release energy for biological work. The organs used for breathing, the pharynx, larynx, trachea, bronchi,lungs and diaphragm. Respiratory system The lung is the essential respiration organ in higher vertebrates (man). The organ without muscle is lungs. The main function of the lungs is the oxygenation of blood and to supply oxygen to it. Lungs Largest vein: Inferior vena cava Largest artery: Abdominal aorta 5. Muscular System Muscles, the organs of the muscular system are the specialised cells which are responsible for the movement and locomotion. They are characterized by properties such as excitability, contractility, extensibility and elasticity.

Muscular system Three types of muscles: Voluntary, involuntary and cardiac Total number of muscles in body:639 (constitutes 43% of the body weight) Smallest muscle: Stapedius Largest muscle: Gluteus maximus (Buttok muscle) Longest muscle: Sartorius 6. The Skeletal System The human skeletal system consists of bones and cartilages of various types. They provide support, surface for the attachment of muscles and protection to many vital organs like brain, heart, eyes etc, also give a definite form and shape to the body. Skeletal system Total number of bones in body: 206 Smallest bone: Stapes (in the middle ear) Longest bone: Femur (Thigh bone) In an infant, there are 33 vertebrae in the vertebral column. Five of these bones eventually fuse to form the sacrum, and four other join to become the coccyx. As a result, an adult vertebral column has 26 vertebrae. 7.

The Nervous System Nervous system consists of central nervous system ( includes brain and spinal cord), peripheral nervous system ( includes cranial nerves and spinal nerves) and autonomic nervous system( Nerve chains on either sides of the vertebral column). Neurons : The structural and functional units of the nervous system.It is the longest cell in the body Nervous system The brain and spinal cord constitute the central nervous system (CNS). The brain is the largest and the most complex part of the nervous system. The brain is enclosed in the cranium and the spinal cord in the vertebral column. Weight of brain: 1220-1400 gms Largest part of the human brain: Cerebrum Length of spinal cord: Average 42-45 cm The peripheral nervous system(PNS) consists of the nerves that arise from the central nervous system and connect it to various body parts.The PNS includes cranial nerves and spinal nerves. There are12 pairs of cranial nerves and 31 pairs of spinal nerves. The cranial nerves (12) include sensory (3), motor (5) and mixed (4) nerves. The spinal nerves are named according to the level from they arise.

There are 8 pairs of cranial nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs sacral nerves and a pair of coccygeal nerve. Longest nerve: sciatic Thinnest and smallest nerve: Trochlear (Pathetic) Largest cranial nerve: Trigeminal 8. Endocrine System Endocrine system are those systems which generally control long term activities of target organs as well as physiological process such as digestion, metabolism, growth, development and reproduction in contrast to more rapid activities under the control of nervous system either directly or indirectly. Endocrine system The endocrine system carries out a wide variety of physiological process through chemical messengers called "hormones". Supreme commander of endocrine regulation: Hypothalamus Glands and Hormones 9. Reproductive System The reproductive system includes reproductive organs, reproductive ducts and accessory structures. The organs which produce sex cells and secrete hormones are called primary sex organs. The development of sex organs (gonads) is influenced by gonadotropins of the anterior pituitary.

The organs which perform important functions in reproduction but neither produce gametes nor hormones are called secondary sex organs Male Reproductive system Reproductive ducts: Epididymis, vas deferens and penis Accessory or secondary glands include a prostrate, two seminal vesicles and two Cowper's gland Volume of semen: 2-4 ml Sperms: 300 million sperms Reproductive ducts: Fallopian tube (Oviduct), uterus and vagina Female reproductive System Accessory or secondary glands: Bartholin's glands or vesticular glands Time of puberty in girl: 13 years of Age Duration menstrual cycle in woman: 28 days Time of ovulation: About 14 days before the onset of next menstruation Egg produced at one time: One Age of Menopause: 45-55 years Gestation period: Approximately 270 days Foetal membranes: chorion, amnion, allantois, yolk sac Placenta: Haemochorial 10. Excretory System The organs and tissues participating in the removal of waste products constitute the excretory system. It includes mainly the urinary system.

The urinary system is concerned with the production, storage and elimination of urine. In addition to the urinary system some other organs such as liver, lungs and skin also function as excretory organs. These organs are called accessory excretory organs. The excretory system of man consists of a pair of kidneys, a pair of ureters,urinary bladder and urethra The two kidneys are not in same level. The right kidney is slightly lower the left kidney, because the right side of the abdominal cavity is occupied by the liver. Size of kidney: 11 cm long, 6cm wide and 5 cm in thickness Weight of kidney: 150 gms Nephrons : The structural and functional units of kidneys. A cross section of the kidney (left) and Nephron (right). Nephrons in each kidney: 1 million (10 lakhs) Length of nephrons: 35-50 mm Urine pH 4.5–8.2 11. Immune System It is a collection of mechanism within an organism that protects aginst diseases by identifying and kiiling pathogens and tumor cells.

It detects a wide variety of agents from viruses to parasitic worms, and needs to distinguish them from the organism’s own healthy cells and tissues in order to function properly.The immune system of vertebraes such as human consists of many types of proteins ( immunoglobulins ), cells, ogans and tissues, which interact in an elaborate and dynamic network . Two types of lymphoid organs : Immune System Primary lympoid organs (Central Lympoid organs) : Thymus and bone marrow Thymus is the site of T lymphocyte maturation and bone marrow is the site of B lymphocytes maturation and are responsible for cellular and humoral immune response respectively. Secondary Lymphoid organs(Peripheral Lymphoid organs) : Lymphnodes, spleen, tonsils, Peyer's patches of the small intestine, appendix and mucousal associated lymphoid tissue (MALT). Learn more:

Question: In the human body, a set of well-developed abdominal muscles is known as a ‘What’…pack’?
Answer: Six